Mobile electronic devices for accessing wireless network is becoming more and more popular, but the power consumption of devices with built-in wireless network function is high, and thus shortens the operation time of mobile electronic devices using batteries for power supply. Several methods for power management of an electronic device are provided in U.S. Pat. No. 6,330,462 B1, U.S. Pat. No. 6,236,674 B1, U.S. Pat. No. 6,489,725 B1, etc. A communication system disclosed in U.S. Pat. No. 6,330,462 B1 manages power by changing a rate of transmitting data. The system includes a transmitter and a receiver. Firstly, the transmitter is operated at an idle rate. Next, the transmitter sends a notice to the receiver when the transmitter receives the data to be transmitted at a high rate. Finally, the transmitter transmits the data to the receiver at a high rate. The method described in U.S. Pat. No. 6,236,674 B1 manages power by mode switching. The transmitter and the receiver can switch between a low-consumption mode and an active mode, and a control circuit controls the switch according to the data detected to be received. The receiver of the method also can include a circuit detecting the strength of the signal to be received. The circuit can disable the receiver circuit when the detected strength of the data to be received is smaller than a predetermined value. The method of U.S. Pat. No. 6,489,725 B1 uses a power saving circuit to save standby power of electronic devices. A capacitor is connected to an AC power supply, and a phase-leading current component passing the capacitor is used to make a DC power supply supplying power during standby. In case an infrared command is used, the capacitor is connected in parallel to another capacitor to strengthen the current output capability of the DC power supply, having an AC switching element maintained in on mode.
However, power consumption for the abovementioned designs is high, and a method and an apparatus for power management to save more power is needed.